Method for detecting servo error, apparatus therefor, disk which maintains quality of servo error signal, method of controlling servo of disk recording/reproducing apparatus, method of detecting tracking error, and method of detecting tilt error

ABSTRACT

An apparatus for recording data on and reproducing data from the disk in which a recording area is divided into sectors, includes a reproducing signal generator for generating a reproducing signal including sum signals V 1  and V 2  of radial pairs, a sum signal RF_sum, and a push-pull signal RF_pp from an optical signal reflected from the disk, a header area detector for generating a header area signal including a header area from the reproducing signal, a first synchronous signal level detector for detecting a magnitude Ivfo 1  of a first synchronous signal in the first header by being synchronized with the header area signal, a second synchronous signal level detector for detecting a magnitude Ivfo 3  of a second synchronous signal in the second header by being synchronized with the header area signal, and a balance calculator for calculating the balance of the magnitude Ivfo 1  and the magnitude Ivfo 3.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/385,472, currently pending, the disclosure of which is incorporatedby reference, which is a divisional of prior application Ser. No.09/629,050, filed Jul. 31, 2000, which issued as U.S. Pat. No.6,556,521, which is a divisional of application Ser. No. 09/385,415,filed Aug. 30, 1999, now U.S. Pat. No. 6,469,979.

This application claims the benefit of Korean Application Nos. 98-35421,filed Aug. 29, 1998, 98-35422, filed Aug. 29, 1998, and 99-8482, filedMar. 13, 1999, in the Korean Patent Office, the disclosures of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical recording/reproducingapparatus for recording digital data on a disk and reproducing digitaldata from a disk, and more particularly, to a method for detecting servoerror by comparing the levels of synchronous signals recorded on theheader area of a disk, an apparatus suitable for the method, a diskwhich guarantees the quality of a push-pull signal which is the basis ofoptimally controlling the servo, a method for controlling the servo ofthe recording/reproducing apparatus, a method for detecting a trackingerror, and a method for detecting a tilt error.

2. Description of the Related Art

The quality of a signal remarkably deteriorates due to a servo errorsuch as the tilt and detrack of a disk as recording density becomeshigher not only in a disk only for reproduction such as a DVD-ROM butalso in a recordable disk such as a DVD-RAM. In particular, in therecordable disk, the recording quality deteriorates due to the influenceof the servo error when the servo error exists during recording and thedeterioration of the quality of the signal becomes severe due to theservo error during the reproduction of a concerned part.

In a DVD-RAM disk, information is recorded on a track. The track iscomprised of a land track and a groove track. The land track and thegroove track alternate when the disk rotates once. The land track andthe groove track are alternated in the DVD-RAM disk in order to providea tracking guide in an initial stage and to reduce crosstalk betweenadjacent tracks in high density narrow tracks.

Each track is comprised of sectors having a uniform length. Apre-embossed header area is provided during the manufacturing of thedisk as a means of physically dividing the sectors. The physicaladdresses of the sectors are recorded in the pre-embossed header area.

Each sector is comprised of a header area in which physicalidentification data (PID) is recorded and a data area.

FIG. 1A shows the physical shape of the land track in a DVD-RAM disk.FIG. 1B shows the waveform of a push-pull signal in the land track.

The header area is repeatedly arranged in every sector of the track.Four PIDs (PID1 through PID4) having the same value are recorded in oneheader area. The PID1 and the PID2 are arranged to deviate from thecenter of the track by a certain amount and the PID3 and the PID4 arearranged to deviate from the center of the track in a direction oppositeto that of the PID1 and PID2 so that the PIDs can be correctly read evenif a laser spot 25 deviates from the center of the track. Also, thearrangements of the PID1 and PID2 and the PID3 and PID4 in the landtrack are opposite to those in the groove track. The push-pull signalshown in FIG. 1B can be obtained in the land track.

FIG. 2A shows the physical shape of the groove track in a DVD-RAM disk.

FIG. 2B shows the waveform of the push-pull signal in the groove track.

FIG. 3 shows the enlarged header area shown in FIGS. 1A and 2A. In thestructure of the header area, the PID1 and PID2 and the PID3 and PID4are arranged to deviate from the center of the track in oppositedirections by a uniform amount. A vfo signal having a specifiedfrequency for synchronizing and detecting ID and an ID signal showingthe physical addresses of the sectors are recorded in the respectivePIDs. The vfo signal has a recording pattern of 4 T (T is a period ofthe clock signal).

As shown in FIG. 3, the header area is comprised of vfo1 33 and ID1(PID1) 34, vfo2 35 and ID2 (PID2) 36, vfo3 37 and ID3 (PID3) 38, andvfo4 39 and ID4 (PID4) 40.

In FIG. 3, when the laser spot passes through the header area of thegroove track, a push-pull signal RF_pp shown in FIG. 4A and a sum signalRF_sum shown in FIG. 4B are obtained. In FIG. 4A, a vfo1 signal 42corresponds to the vfo1 signal area 33 of FIG. 3. A vfo3 signal 43corresponds to the vfo3 signal area 37.

FIG. 5 shows the structure of an apparatus for obtaining the push-pullsignal shown in FIG. 4A and the sum signal shown in FIG. 4B. In FIG. 5,reference numeral 50 denotes a photodetector divided into four sections.Reference numerals 52 and 54 denote adders. Reference numeral 56 denotesa calculator.

The apparatus shown in FIG. 5 outputs the sum signal RF_sum of signalsdetected by light receiving elements A through D of the photodetectordivided into four, sum signals V1 and V2 of radial pairs B and C, and Aand D of respective light receiving elements, and the push-pull signalRF_pp which is a subtraction signal V2−V1 of V1 and V2.

FIG. 10 shows a conventional technology for compensating for tilt and amethod for detecting the amount of tilt by a specific pattern recordedon the track of a disk. The specific pattern coincides with theproceeding direction of the track and the center of the track and isrealized in the form of a reference pit A and/or a reference pit B.

It is possible to obtain tilt information by comparing signalsreproduced from the reference patterns shown in FIG. 10 with each otherand to thus operate tilt compensating equipment according to theobtained tilt information or to compensate for the signals by changingthe equalizer coefficient of the reproducing signal.

The reference patterns shown in FIG. 10 are located in an arbitraryposition in the disk and are useful for detecting tangential tilt (tiltin a track direction).

However, in the conventional technology shown in FIG. 10, the length ofthe reference pattern for detecting the tilt is too short. Anotherpattern is necessary in order to detect the correct position of the tiltpattern. Also, radial tilt (tilt in a radial direction) cannot bedetected. Since the radial tilt is larger than the tangential tilt inpractice, the reference patterns are not so useful.

Since it is necessary to precisely manage the servo for therecording/reproducing apparatus to maintain an optimalrecording/reproducing state, it is necessary to manage the servo errorsignal in high resolution.

However, the precision of the servo error signal varies depending on thedisk or the reproducing apparatus. Accordingly, it is difficult toprecisely manage the servo.

SUMMARY OF THE INVENTION

To solve the above problem, it is a first object of the presentinvention to provide an improved method of detecting a servo error.

It is a second object of the present invention to provide an apparatusfor detecting a servo error suitable for the above method.

It is a third object of the present invention to provide a disk havingan improved specification for maintaining the quality of a reproducingsignal which is the basis of optimally controlling a servo.

It is a fourth object of the present invention to provide a method ofcontrolling the servo of a recording/reproducing apparatus.

Additional objects and advantages of the invention will be set forth inpart in the description which follows and, in part, will be obvious fromthe description, or may be learned by practice of the invention.

Accordingly, to achieve the first and other objects of the presentinvention, there is provided a method of detecting servo error of anapparatus for recording data on and reproducing data from a disk in adata area of which reference patterns having a uniform size arerecorded, wherein the servo error of the recording/reproducing apparatusis detected by the ratio of the magnitude of the reference patternsrecorded on at least two positions separated from each other to themagnitude of the reproducing signal corresponding to the referencepatterns.

To achieve the second and other objects of the present invention, thereis provided an apparatus for recording data on and reproducing data froma disk in which a recording area is divided into sectors, each sectorhas a header for notifying an address, each header has a first headerand a second header which are recorded to deviate from the center of atrack in opposite directions, and the first header and the second headereach have address areas in which the addresses of sectors are recordedand synchronous signal areas in which synchronous signals for detectingthe address signals recorded in the address area are recorded, theapparatus comprising a reproducing signal generator for generating areproducing signal including sum signals V1 and V2 of radial pairs, asum signal RF_sum, and a push-pull signal RF_pp from an optical signalreflected from the disk, a header area detector for generating a headerarea signal comprising a header area from the reproducing signalreceived from the reproducing signal generator, a first synchronoussignal level detector for receiving the output of the reproducing signalgenerator and detecting a magnitude Ivfo1 of a synchronous signal in thefirst header by being synchronized with the header area signal receivedfrom the header area detector, a second synchronous signal leveldetector for receiving the output of the reproducing signal generatorand detecting a magnitude Ivfo3 of a synchronous signal in the secondheader by being synchronized with the header area signal received fromthe header area detector, and a balance calculator for calculating thebalance of the magnitude Ivfo1 of the first synchronous signal detectedby the first synchronous signal level detector and the magnitude Ivfo3of the second synchronous signal detected by the second synchronoussignal level detector.

To achieve the third and other objects of the present invention, thereis provided a disk in which, when the magnitude of a synchronous clocksignal in a peak header is Ivfo1 and the magnitude of the synchronousclock signal in a bottom header is Ivfo3, the ratio of the magnitude ofIvfo1 to the magnitude of Ivfo3 has a predetermined restricted value.

To achieve the fourth and other objects of the present invention, thereis provided a method of controlling a servo in which, when the magnitudeof the synchronous clock signal in the peak header is Ivfo1 and themagnitude of the synchronous clock signal in a bottom header is Ivfo3,tilt is controlled so that the ratio of the magnitude of Ivfo1 to themagnitude of the Ivfo3 satisfies a predetermined restricted value.

BRIEF DESCRIPTION OF THE DRAWINGS

The above object and advantages of the present invention will becomemore apparent by describing in detail a preferred embodiment thereofwith reference to the attached drawings, in which:

FIG. 1A shows the physical shape of a land track;

FIG. 1B shows the waveform of a push-pull signal in the land track;

FIG. 2A shows the physical shape of a groove track;

FIG. 2B shows the waveform of a push-pull signal in the groove track;

FIG. 3 shows an enlarged header area shown in FIGS. 1A and 2A;

FIGS. 4A and 4B show a push-pull signal and a sum signal which areobtained when a laser spot passes through the header area of the groovetrack in FIG. 3;

FIG. 5 shows the structure of an apparatus for obtaining the reproducingsignal shown in FIG. 4;

FIG. 6 is a block diagram showing a structure of an apparatus fordetecting a servo error according to an embodiment of the presentinvention;

FIGS. 7A through 7E show waveforms generated during the operation of theapparatus shown in FIG. 6;

FIG. 8 is a block diagram showing a structure of an apparatus fordetecting the servo error according to another embodiment of the presentinvention;

FIGS. 9A through 9B show waveforms generated during the operation of theapparatus shown in FIG. 8;

FIG. 10 shows a conventional technology for correcting tilt;

FIG. 11 is a graph showing the relationship between radial tilt and abalance value K in the method and apparatus according to the presentinvention; and

FIG. 12 is a graph showing the relationship between detrack and thebalance value K in the method and apparatus according to the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now made in detail to the present preferred embodimentsof the present invention, examples of which are illustrated in theaccompanying drawings, wherein like reference numerals refer to the likeelements throughout. The embodiments are described below in order toexplain the present invention by referring to the figures.

For example, in a push-pull signal, the ratio of the magnitude of thesignal PID1 and PID2 to the magnitude of the signal PID3 and PID4 variesby up to 30%, depending on the disk. When such signals are used asreference signals for controlling a servo, it is difficult to preciselymanage the servo and maintain optimal recording/reproducing states.

In a method for detecting the servo error according to an embodiment ofthe present invention, a servo error is detected by the ratio of themagnitude of reference patterns regularly recorded on a disk to themagnitude of a reproducing signal corresponding to the referencepatterns. Reference patterns could include a synchronous signal recordedin a header area and a wobble signal recorded in the direction of atrack of a disk.

First, a method of detecting the servo error using the synchronoussignal recorded in the header area will be described. When the opticalaxis of a laser spot is vertical to the header area, namely, when tiltin a radial direction does not occur, the magnitude (Ivfo1) of adetected vfo1 signal is approximately equal to the magnitude (Ivfo3) ofa vfo3 signal. However, in the case that tilt or detrack occurs, wheneither the Ivfo1 or the Ivfo3 becomes large, the other becomes small.The tilt in the radial direction denotes a case in which the disk isslanted in the radial direction of the disk, and the tilt in atangential direction denotes a case in which the disk is slanted in atracking direction of the disk. The directions made by the radial tiltand the tangential tilt are offset by 90°.

This is because the intensity of light reflected from the PID1 and PID2and the PID3 and PID4, which are arranged to deviate from the center ofthe track in opposite directions, varies in relation to the tilt of thedisk although the light spot tracks the center of the track. When thedisk is tilted to an inner side, the intensity of light reflected froman upper header (a peak header) is larger than that reflected from alower header (a bottom header) as shown in FIGS. 1A through 2A. For thedescription of this disclosure, the disk is divided into an inner sideand an outer side with respect to the position of an optical pickup (notshown). Thus, the inner side is from the position of the optical pickupto the center of the disk and the outer side is from the position of theoptical pickup to the edge of the disk.

Accordingly, the ratio of the magnitude Ivfo1 of the vfo1 signal to themagnitude Ivfo3 of the vfo3 signal varies. Also, the ratio of themagnitude Ivfo2 of a vfo2 signal to the magnitude Ivfo4 of a vfo4 signalvaries.

In order to detect the degree to which the magnitude ratio varies, asignal recorded at a uniform level should be used. Since vfo signalshave uniform recording levels and frequencies, the vfo signals aresuitable for this purpose. The vfo signals are similar to servo burstsignals in a hard disk drive and are physically recorded on the disk.The vfo signals are recorded on the disk at a uniform level, but thesize of the signals reproduced from the region of the vfo signals isaffected by tilt. Also, it is easier to detect the magnitude of the vfo1and vfo3 signals than that of the vfo2 and vfo4 signals.

Here, when the magnitudes of the synchronous signals detected in thevfo1 and vfo3 areas are Ivfo1 and Ivfo3, respectively. A balance value Kis defined as follows.K=(Ivfo ₁ −Ivfo ₃)I(Ivfo ₁ +Ivfo ₃)  (1)orK=(Ivfo ₁ −Ivfo ₃)/Io  (2)wherein, lo is the magnitude of the sum signal RF_sum in the mirrorarea.

In Equations 1 and 2, the balance value K is calculated using themagnitude of the synchronous signals detected from the areas vfo1 andvfo3. While it is possible to calculate the balance value K using themagnitude of the synchronous signals detected from the areas vfo2 andvfo4, it is easier to detect the synchronous signals from the areas vfo1and vfo3 than from the areas vfo2 and vfo4. Also, it is possible to usethe value obtained by the combination of the synchronous signalsdetected in the areas vfo1 and vfo2 and the value obtained by thecombination of the synchronous signals detected in the areas vfo3 andvfo4.

When the balance value K obtained in the case that there is no servoerror is K_(o), and the balance value K obtained in the case that aservo error exists is K₁, the difference between the two values isdefined as follows.K _(t) =K _(o) −K ₁  (3)

Namely, it is possible to know the direction and magnitude of the servoerror according to the value and sign of K_(t).

Here, K_(o) may be the value measured in a state where there is no servoerror, a default value determined by the system controller of arecording/reproducing apparatus, or a value measured in a referencestate determined by the system.

In the land track and the groove track, the polarity of K₁ should varyin order to calculate K_(t) correctly since the position of PID1 andPID2 and the position of PID3 and PID4 are inversed.

A method of detecting the servo error of the disk using the wobblesignal will now be described. Wobble is formed in the land track and thegroove track in the DVD-RAM disk. The wobble is in the form of asinusoidal wave formed on the side wall of the track.

When the disk is tilted in a radial direction, the wobble signal istilted in the radial direction. Namely, the magnitude of the wobblesignal varies between two arbitrary points separated from each other inthe radial direction. Therefore, it is possible to detect tilt bydetecting the amount of change of the wobble signal in the radialdirection.

FIG. 6 is a block diagram showing the structure of an apparatus fordetecting the servo error signal according to an embodiment of thepresent invention. The apparatus shown in FIG. 6 includes a reproducingsignal generator 62, a header area detector 64, a first synchronoussignal level detector 66, a second synchronous signal level detector 68,a balance calculator 70, a comparator 72, a land/groove detector 76, atilt controller 74, a polarity inverter 78, and a detrack compensator80.

The reproducing signal generator 62 generates a sum signal RF_sum, sumsignals V1 and V2 of radial pairs, and a push-pull signal RF_pp obtainedby subtracting V1 from V2. The reproducing signal generator 62 includesthe photodetector divided into four and a calculator as shown in FIG. 5.

The header area detector 64 generates header area signals (a header areasignal 1 and a header area signal 2) showing the header area from thereproducing signal. Here, the header area signal 1 is determined fromthe PID1 and PID2 areas. The header area signal 2 is determined from thePID3 and PID4 areas. Since the header area has an envelope larger thanthat of the data area, it is possible to obtain a header area signalshowing the header area using both an envelope detector for detectingthe envelope of the reproducing signal and a comparator.

The first synchronous signal level detector 66 synchronized with theheader area signal 1 generated by the header area detector 64 detectsthe magnitude Ivfo1 of the vfo1 signal shown in FIG. 4. To be specific,a first enable signal (enable 1) having a predetermined width andseparated from the starting point of the header area signal 1 by apredetermined distance is generated. After gating the reproducing signalby the first enable signal (enable 1), the magnitude Ivfo1 of the vfo1signal is detected by detecting the peak-to-peak value of the gatedreproducing signal.

The second synchronous signal level detector 68 synchronized with theheader area signal 2 generated by the header area detector 64 detectsthe magnitude of the vfo3 signal shown in FIG. 4. To be specific, themagnitude Ivfo3 of the vfo3 signal is detected by generating a secondenable signal (enable 2) having a predetermined width and separated fromthe starting point of the header area signal 2, gating the reproducingsignal by the second enable signal (enable 2), and detecting thepeak-to-peak value of the gated reproducing signal.

The balance calculator 70 calculates the ratio of the magnitude Ivfo1 ofthe vfo1 signal detected by the first synchronous signal level detector66 to the magnitude Ivfo3 of the vfo3 signal detected by the secondsynchronous signal level detector 68 as shown in Equation 1. Here, thebalance calculator 70 can output the mean value of the balance valuesobtained from several successive sectors in the radial or tangentialdirection.

The comparator 72 compares the balance value K₁ calculated by thebalance calculator 70 with a predetermined reference value K_(o) andoutputs the difference between the two values K_(t) as shown in Equation3. Here, K may be a value measured in a state where there is no tilt, adefault value determined by the system controller of therecording/reproducing apparatus, or a value measured in the referencestate determined by the system. The value K_(o) is a predeterminedconstant for calculation of K₁ and determined to be identical toEquations 1 and 2. In an ideal disk in which the levels of recorded vfosignals are substantially the same and there is no tilt, K_(o) becomes“0” in Equations 1 and 2. However, in an actual disk, as the ends ofrecorded vfo signals are not identical, K_(o) does not become “0.”

The land/groove detector 76 receives the reproducing signal and detectswhether the current track is a land track or a groove track. In thepush-pull signal of the land track, the magnitude of the PID1 and PID2is smaller than that of PID3 and PID4 as shown in FIG. 1B. In thepush-pull signal of the groove track, the magnitude of PID1 and PID2 islarger than the magnitude of the PID3 and PID4 as shown in FIG. 2B. Theland/groove detector 76 discriminates the land track from the groovetrack using the above procedure.

The polarity inverter 78 inverts the polarity of the subtraction valueK_(t) output from the comparator 72 according to the result detected bythe land/groove detector 76.

The balance value can be used in order to compensate for tilt.

The tilt controller 74 controls the tilt of the disk according to thesubtraction value K_(t) the polarity of which is inverted and which isoutput from the polarity inverter 78. Since the sign and magnitude ofthe subtraction value K_(t) show the direction and magnitude of thetilt, the tilt of the disk is controlled by feeding back the sign andthe magnitude of the subtraction value K_(t).

The balance value can be used in order to correct detrack.

The detrack compensator 80 controls the detrack of the disk according tothe subtraction value K_(t) the polarity of which is inverted and whichis output from the polarity inverter 78. Since the sign and magnitude ofthe subtraction value K_(t) shows the direction and magnitude of thedetrack, the detrack of the disk is controlled by feeding back thesubtraction value K_(t).

The resolution of the sign and magnitude of the subtraction value K_(t)varies depending upon the signal used (see the description relating toFIGS. 11 and 12, et seq.)

FIGS. 7A through 7E show the waveforms generated by the operation of theapparatus shown in FIG. 6. FIG. 7A shows the waveform of the push-pullsignal generated by the reproducing signal generator 62. FIGS. 7B and 7Cshow the waveforms of the header area signal 1 and the header areasignal 2, respectively, generated by the header area detector 64. FIGS.7D and 7E show the waveforms of the first enable signal (enable 1) andthe second enable signal (enable 2) used by the first synchronous signallevel detector 66 and the second synchronous signal level detector 68respectively.

FIG. 8 is a block diagram showing a structure of an apparatus forgenerating the servo error signal according to another embodiment of thepresent invention. The apparatus shown in FIG. 8 is similar to theapparatus shown in FIG. 6, except that the apparatus shown in FIG. 8includes a mirror area signal generator 86 and a mirror signal leveldetector 88. Therefore, the same reference numerals are used for thesame members and a detailed description thereof is omitted.

The mirror area signal generator 86 generates a mirror area signalshowing a mirror area from the sum signal RF_sum provided by thereproducing signal generator 62. In the push-pull signal RF_pp, sincethe mirror signal becomes zero, it is not possible to obtain the mirrorarea signal by the push-pull signal RF_pp.

It is possible to generate the mirror area signal by the envelopedetector and the comparator since the mirror signal has a much lowerenvelope than the signals of the data area and the header area.

The mirror signal level detector 88 detects the level of the mirrorsignal obtained from the sum signal RF_sum and output by the mirror areasignal generator 86. The mirror signal level detector 88 generates athird enable signal (enable 3) having a period according to the mirrorarea signal generated by the mirror area signal generator 86, gates thesum signal RF_sum by the third enable signal (enable 3), and detects thepeak-to-peak value of the gated sum signal RF_sum, to generate a mirrorsignal level lo.

The balance calculator 72 calculates the balance value K₁ as shown inEquation 2 based upon the level Ivfo1 of the vfo1 signal detected by thefirst synchronous signal level detector 66, the level Ivfo3 of the vfo3signal detected by the second synchronous signal level detector 68, andthe mirror signal level lo detected by the mirror signal level detector88. Here, the balance calculator 72 can output the mean value of thebalance values obtained from several successive sectors in the radial ortangential direction.

FIGS. 9A and 9B show waveforms generated during the operation of theapparatus shown in FIG. 8. FIG. 9A shows the waveform of the mirror areasignal output from the mirror area signal generator 86. FIG. 9B showsthe waveform of the third enable signal (enable 3).

According to the present invention, it is possible to use the push-pullsignal RF_pp, the sum signals V1 and V2 of the radial pairs, and the sumsignal RF_sum for detecting the servo error since the servo error isdetected by the balance value of the synchronous signals. For example,when the push-pull signal RF_pp is used, it is possible to compensatefor tilt in the radial direction. When the sum signal RF_sum is used, itis possible to compensate for tilt in the tangential direction.

FIG. 11 is a graph showing the relationship between the radial tilt andthe balance value K in the methods and apparatuses according to theembodiments of the present invention. In FIG. 11, the horizontal axisdenotes radial tilt values and the vertical axis denotes balance valuesK. In FIG. 11, the graph marked with ▴ shows a case where the sum signalRF_sum and the balance value according to Equation 1 are used. The graphmarked with ▾ shows a case where the sum signal RF_sum and the balancevalue according to Equation 2 are used. The graph marked with ● shows acase where the push-pull signal RF_pp and the balance value according toEquation 2 are used. The graph marked with ▪ shows a case where thepush-pull signal RF_pp and the balance value according to Equation 1 areused.

As shown in FIG. 11, the radial tilt is best described by the casemarked with ▪ where the push-pull signal RF_pp and the balance valueaccording to Equation 1 are used. The case marked with ● where thepush-pull signal RF_pp and the balance value according to Equation 2 areused is also useful for describing the radial tilt.

Therefore, it is possible to determine the tilt by the values accordingto Equations 1 and 2 using the push-pull signal RF_pp.

FIG. 12 is a graph showing the relationship between the detrack and thebalance value K in the methods and apparatuses according to theembodiments of the present invention. In FIG. 12, the horizontal axisdenotes the amount of the detrack. The vertical axis denotes the balancevalue K. In FIG. 12, the graph marked with ▴ shows a case where the sumsignal RF_sum and the balance value according to Equation 1 are used.The graph marked with ▾ shows a case where the sum signal RF_sum and thebalance value according to Equation 2 are used. The graph marked with ●shows a case where the push-pull signal RF_pp and the balance valueaccording to Equation 2 are used. The graph marked with ▪ shows a casewhere the push-pull signal RF_pp and the balance value according toEquation 1 are used.

As shown in FIG. 12, the graph marked with ▴ shows the case where thesum signal RF_sum and the balance value according to Equation 1 is mostaffected by the detrack. The graph marked with ▪ shows the case wherethe push-pull signal RF_pp and the balance value according to Equation 1is least affected by the detrack.

Therefore, it is possible to determine the detrack by the valueaccording to Equation 1 or 2 using the sum signal RF_sum.

The quality of the servo error signal varies according to the quality ofthe disk and the conditions of the system. However, when the value ofthe servo error signal is not restricted to some degree, it is notpossible to recognize the PIDs or it is difficult to stably manage theservo. Therefore, in the disk, the value K_(o) is preferably managed tomaintain a prescribed level.

Accordingly, in the present invention, it is suggested that the valueK_(o) be restricted to ±0.1. This value is required to normallyreproduce each PID when a standard amount of tilt ±0.35° is given. Also,the allowance range of the track control is considered.

Also, it is necessary to restrict the value K_(t) to no more than apredetermined value to precisely control the servo in the apparatus forreproducing data from the disk. When the quality of the servo is notstrictly managed when the data is reproduced, it is not possible toobtain the PID information.

Therefore, in the present invention, it is suggested that the valueK_(t) be restricted to ±0.1 in the servo operation of the reproducingapparatus.

It is possible to correctly detect the tilt state of the disk without aspecific pattern for detecting the servo error by the method fordetecting the servo error according to the present invention.

It is possible for the recording/reproducing apparatus to stably controlthe servo and to maintain an optimal recording/reproducing state sincethe apparatus for generating the servo error signal according to thepresent invention correctly detects the servo error state of the disk.

It is possible for the recording/reproducing apparatus to stably controlthe servo and to maintain the optimal recording/reproducing state sinceit is possible to strictly manage the level of the servo error signalwhich is the basis of controlling the servo by the disk according to thepresent invention.

Although a few preferred embodiments of the present invention have beenshown and described, it would be appreciated by those skilled in the artthat changes may be made in this embodiment without departing from theprinciples and spirit of the invention, the scope of which is defined inthe claims and their equivalents.

1. An apparatus to detect a servo error of a recording and/orreproducing apparatus for recording the data on and/or reproducing datafrom a disk having a data area divided into sectors, each sector has aheader comprising an address, each header has a first header and asecond header which are recorded to deviate from a center of the trackin opposite directions, and the first header and the second header haveaddress areas having address signals of the sectors and synchronoussignal areas having synchronous signals for detecting the addresssignals recorded in the address areas, the apparatus comprising: adetector to detect a first magnitude of the synchronous clock signaldetected from the first header as Ivfo1 and a second magnitude of thesynchronous clock signal detected from the second header as Ivfo3; and asignal processor to generate a sum signal RF_sum; and a controller tocontrol an orientation of the disk relative to the recording and/orreproducing apparatus such that a ratio of the first magnitude Ivfo1 tothe second magnitude Ivfo3 has predetermined restricted value.
 2. Theapparatus of claim 1, wherein a magnitude of the ratio is no more than±0.1.
 3. The apparatus of claim 2, wherein the first and secondmagnitudes Ivfo1 and Ivfo3 are detected by a photo detector havingradial pairs of detecting elements, and are detected from a subtractionsignal RF_pp of the radial pairs of the detecting elements.
 4. Theapparatus of claim 2, wherein the first and second magnitudes Ivfo1 andIvfo3 are detected by a photo detector having radial pairs of detectingelements, and are detected from the sum signal RF_sum of the radialpairs of the detecting elements.
 5. The apparatus of claim 1, wherein amagnitude of the ratio is determined to be (Ivfo1−Ivfo3)/lo, wherein lois a magnitude of a mirror signal.
 6. The apparatus of claim 5, whereinthe first and second magnitudes Ivfo1 and Ivfo3 are detected by a photodetector having radial pairs of detecting elements, and are detectedfrom a subtraction signal RF_pp of the radial pairs of the detectingelements.
 7. The apparatus of claim 5, wherein the first and secondmagnitudes Ivfo1 and Ivfo3 are detected by a photo detector having pairsof detecting elements, and are detected from the RF_sum of the radialpairs of detecting elements.